Plasma type spray powder alloys of nickel, cobalt, chromium, aluminum, and yttrium are used extensively in the aircraft industry for high temperature corrosion resistant coatings. It is desirable that these powders be of from about 15 to about 44 microns in size and have uniform spherical shape for optimum processing.
These alloys are produced by conventional atomization processes from liquid melts. Because these materials require a low oxygen content, melting must be performed in an inert gas environment. Typical inert gas atomized powders have a rather broad particle size distribution. Therefore, the yield of in-size material which is usable for plasma spray applications is only a fraction of the powder atomized.
A process for forming alloy powders for plasma spray applications is disclosed in an article entitled "Low-Pressure Plasma-Deposited Coatings Formed From Mechanically Alloyed Powders" by J. R. Rairden and E. M. Habesch of General Electric Corporate Research and Development, published in "Thin Solid Films", accepted Apr. 10, 1981. The process of this article involves mechanical dry and wet milling of powders. Such mechanically produced alloys are not completely uniform in size. Furthermore, such alloy powders are irregular in shape.
Therefore, a process for producing a high yield of in-size particles of spherical shape and well alloyed composition for plasma spray applications would be an advancement in the art.